Guide - Built-In Game for the TurboGrafx

[TailChao]

I was doing some rework on my TurboGrafx and decided to poke around at the unpopulated chip pads for IC107 and IC108 near the HuCard slot.

I've seen literature claiming these may have been intended for a built-in game. But after tracing back the pinout of both chips it looks more like IC107 was just supposed to contain a small instruction screen which is displayed when you start the console without a card (like the Master System). IC108 controls the mapping, and probably was just supposed to obfuscate the address line mapping of IC107 to make it more difficult to install stolen software.

But that's just a guess.

Anyway, with some work we can install our own built-in game up to 8 MEGA POWER in size. What we're going to do is adapt the original socket to hold a 27C801 compatible chip and add a small circuit to activate this ROM if and only if a HuCard isn't inserted. I'd rate this at moderate difficulty if you'd like to try, i.e. you should have some basic electronics knowledge and steady hands.

Let's do some soldering.

Here's the pinout for IC107 :

Code: [Select]

                 IC107
              _____ _____
         VCC | 1   v  32 | VCC
         OEn | 2      31 | R139 *
         GND | 3      30 | GND
         GND | 4      29 | GND
 ** IC108,18 | 5   2  28 | GND
 ** IC108,19 | 6   3  27 | IC108,17 **
 ** IC108,20 | 7   C  26 | IC108,16 **
 ** IC108,21 | 8   1  25 | GND
 ** IC108,22 | 9   0  24 | GND
          A2 | 10  0  23 | GND
          A1 | 11  0  22 | IC108,15 **
          A0 | 12  E  21 | D7
          D0 | 13     20 | D6
          D1 | 14     19 | D5
          D2 | 15     18 | D4
         GND | 16     17 | D3
             |___________|

  * R139 isn't populated, so this is NC'd.
    Looks like it was just supposed to be a pullup.

 ** IC108 isn't populated, so these are NC'd.


We need to modify it like this :

Code: [Select]

                                         IC107
                                      _____ _____
              *** A19 (HuCard Pin 3) | 1   v  32 | VCC
              *** A16 (HuCard Pin 4) | 2      31 | A18 (HuCard Pin 33)
              *** A15 (HuCard Pin 5) | 3      30 | A17 (HuCard Pin 32) ***
              *** A12 (HuCard Pin 6) | 4      29 | A14 (HuCard Pin 31) ***
  **** A7 (HuCard Pin 7) <- IC108,18 | 5      28 | A13 (HuCard Pin 30) ***
  **** A6 (HuCard Pin 8) <- IC108,19 | 6   2  27 | IC108,17 -> A8 (HuCard Pin 29)
  **** A5 (HuCard Pin 9) <- IC108,20 | 7   7  26 | IC108,16 -> A9 (HuCard Pin 28)
 **** A4 (HuCard Pin 10) <- IC108,21 | 8   C  25 | A11 (HuCard Pin 27) ***
 **** A3 (HuCard Pin 11) <- IC108,22 | 9   8  24 | OEn (HuCard Pin 26) ***
                                  A2 | 10  0  23 | A10 (HuCard Pin 25) ***
                                  A1 | 11  1  22 | IC108,15 -> GAME_CSn
                                  A0 | 12     21 | D7
                                  D0 | 13     20 | D6
                                  D1 | 14     19 | D5
                                  D2 | 15     18 | D4
                                 GND | 16     17 | D3
                                     |___________|

  *** Original trace must be cut.

 **** You can also just reconnect these address pins on IC108's pad.
      A7 == IC108,18 -> IC108,64
      A6 == IC108,19 -> IC108,63
      A5 == IC108,20 -> IC108,62
      A4 == IC108,21 -> IC108,61
      A3 == IC108,22 -> IC108,60

The circuit to enable the internal game (GAME_CSn) when a card isn't inserted can be two NAND gates using A20 (HuCard Pin 24) and CARDn (HuCard Pin 1).

Code: [Select]

GAME_CSn = !(!(A20 & A20) & CARDn)

This can be implemented with a single 74LS00. Below are two photos of my board to give an idea of how much stuff you'll have to add.





Keep in mind some of the patch wires here are for different repairs or from when I was reverse engineering stuff. Basically, doing this won't make such a huge mess.

[HuMan]

If I actually had a TG16, this would be fun to do.

[Necromancer]

Heh, that's pretty neat.  Looks like a relatively clean install and I'm surprised you can fit all those kangaroos in.

[TailChao]

Heh, that's pretty neat.  Looks like a relatively clean install and I'm surprised you can fit all those kangaroos in.

I was considering putting a System Card 2.0 in there so it'd be just like owning a Duo except worse, but the kangaroos are a way better resident. Best option is probably to install Magical Chase and flip the thing on eBay so I can buy a few cars.

Anyway, TurboGrafx is all put back together.

No game inserted gives you Kangaroo Mans '94.


Putting a card in will run that instead.


CD Stupid Cards and rare sharpie-edition games are still fine.

[Necromancer]

So are those empty spots only on the TG-16 (and maybe PAL TG) or are they on all the PCEs, Duos, Shuttles, etc. too?

[TailChao]

So are those empty spots only on the TG-16 (and maybe PAL TG) or are they on all the PCEs, Duos, Shuttles, etc. too?

As far as I know they’re only in NTSC TurboGrafen.

[Black Tiger]

This is very cool.

Magical Chase gouging is never a joke. The first time I saw this done to a TG-16, it was an ebay listing someone posted here. It was sold as a 'rare" one of a kind unit with Magical Chase built-in.

I'd love to have one made with a homebrew rom like Atlantean and dye/paint it blue to match. Maybe change the logo to Aetherbyte-16 or something.

[Ergot_Cholera]

This is amazing stuff. I wish I still had my PAL Turbografx to check for the empty pads.

P.S. I like your wood.

[TheClash603]

Step 1: Port Stroker to TG16.
Step 2: Install as built-in game.
Step 3:  Sell on eBay without listing built-in game.
Step 4:  Positive feedback.

[TailChao]

Magical Chase gouging is never a joke. The first time I saw this done to a TG-16, it was an ebay listing someone posted here. It was sold as a 'rare" one of a kind unit with Magical Chase built-in.

That's ridiculous. I do remember seeing another TurboGrafx with this modification though, so maybe it was that one.

I'd love to have one made with a homebrew rom like Atlantean and dye/paint it blue to match. Maybe change the logo to Aetherbyte-16 or something.

That could be pretty nice. There's been enough decorated consoles given away in Kickstarters and such that don't have the game they're promoting built-in.

This is amazing stuff. I wish I still had my PAL Turbografx to check for the empty pads.

The PAL board photos I've seen just have a big ground plane where the pads were, but that doesn't mean they're all that way.

P.S. I like your wood.

At first I thought you meant the television. But yeah, the floor is nice too.

[Vecanti]

Is it possible this was going to be for a built in System card?

[TailChao]

Is it possible this was going to be for a built in System card?

I don't think so, at least if the data were only going to be stored in IC107. Enough of the address pins are grounded that a 27C1000 compatible ROM would only be able to contain 1KB of data.

[seieienbu]

I remember the Magical Chase TG auction from a while ago and I recall thinking that it was interesting.  I'm glad I see how it was actually done, finally.  This is really cool.

Yeah, even if it's only system card 2.0 that still seems to be the best option unless you're looking to hawk magical chase and buy an island.  I think a new startup screen before whatever game loads would be kinda neat too.